In orthogonal frequency division multiplexing (OFDM), if a certain symbol contains a delay component, the delay component becomes an interference wave against the subsequent symbol, resulting in a decline of a signal to interference and noise ratio (SINR) of the subsequent symbol. In order to prevent this, a guard interval (GI) is provided at the head of the symbol.
In Patent Document 1, there is described a technology of controlling a guard interval length in accordance with an amount of the delay component. In general, the SINR increases as the guard interval becomes longer, but this causes the communication rate to decrease. With this technology, the guard interval length is so determined that a minimum-required SINR can be obtained to maximize the communication rate.
Further, in Patent Document 2, there is disclosed a technology of reducing, in a case where the same sub-carriers are transmitted from a plurality of transmission devices (for example, at the time of handover), interference between symbols that are transmitted from each of the transmission devices. Further, in Patent Document 3, there is disclosed a technology of improving frequency usage efficiency in OFDM.
Patent Document 1: JP 2002-374223 A
Patent Document 2: JP 2005-303826 A
Patent Document 3: JP 2005-252886 A